To date, the field of industrial decreasing has mainly been such that solvents such as fluorocarbon-based solvents, organic solvents, and oil-based solvents are used, and degreasing is carried out by causing oil content to be dissolved in these solvents. For example, a cleaning device disclosed in Patent Document 1 is a cleaning device that removes a paste adhering to a mouthpiece, wherein organic solvents such as ketones or alcohols are used as cleaning fluids in two cleaning tanks, one each for a rough clean and a finishing clean.
In Patent Document 1, air bubbles having a diameter of in the region of 1 mm to 10 mm are sprayed into a first cleaning tank with an object of agitating and churning the cleaning fluid, and furthermore, an ultrasonic wave is applied to the cleaning fluids in both the first cleaning tank and a second cleaning tank using ultrasonic wave radiation means installed in bottom portions of the cleaning tanks. By a cleaning target being irradiated with an ultrasonic wave, a cavitation phenomenon occurs on a surface of the cleaning target, and dirt such as oil adhering to the cleaning target is decomposed and detached.
However, there are problems that place a heavy burden on the environment, in that solvents such as fluorocarbon-based solvents, organic solvents, and oil-baaed solvents include substances that cause environmental damage such as destruction of the ozone layer and pollution of rivers, oceans, and groundwater, used cleaning fluid has to be processed as industrial waste when replacing the cleaning fluid, and the like. Because of this, there is a demand for cleaning technology that places little burden on the environment to foe developed to replace cleaning using the aforementioned solvents.
Microbubble cleaning wherein microscopic air bubbles of a diameter of ten micrometers to several tens of micrometers are generated in a cleaning fluid based on water, and caused to act on a cleaning target, is attracting attention as cleaning technology that places little burden on the environment. When the microscopic air bubbles are caused to act on the cleaning target, impurities adhering to the surface of the cleaning target, are adsorbed onto the surfaces of the microscopic air bubbles, and line impurities are removed by the microscopic air bubbles separating from the cleaning target under their own buoyancy. A nonionic surfactant with a specific structure is proposed in Patent Document 2 as a surfactant highly effective in stabilizing desired microscopic air bubbles tor a long time.